Baur, R. & N.E. Rank. 1996. Influence of host quality and natural enemies on the life history of the alder leaf beetles Agelastica alni and Linaeidea aenea. Chrysomelidae Biology, P.H.A. Jolivet & M. Cox, editors. Volume 2: Ecological Studies. pp. 173-194. SPB Publishing, Amsterdam.

The univoltine chrysomelids Agelastica alni and Linaeidea aenea both feed on Alnus spp. (Betulaceae). Their habitats and life histories broadly overlap. We compare the presently known data on the life history of these species, the effects of damage-induced changes in food quality on them, and their interactions with natural enemies. The time for larval development, a critical period of exposure to natural enemies, is greater in A. alni than in L. aenea. In addition, damage-induced phytochemical and morphological changes in the alder foliage had substantial negative effects on the host preference and performance of A. alni, but little effect on L. aenea. The most pronounced differences were found for fecundity.

Both beetle species possess chemical defenses. However, the defense of A. alni appears to be more effective against natural enemies. Many generalist predators, including the important syrphid fly predator of L. aenea, Parasyrphus nigritarsus, avoid A. alni entirely. Field studies confirmed that losses to P. nigritarsus are a major mortality factor in L. aenea. The differing ecological strategies of these two leaf beetles provide a basis for studies about the relative importance of the food resource versus the impact of natural enemies on the fitness of these herbivores.

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